I just changed the fuel filter on an Exmark 52" 27hp Kohler. When I cranked it up ran smooth. I finished cutting but when I went to some heavier grass it would bog down and stall. It would start right back up, sound good, good rpm, smooth, but when I took it into the heavier grass it bogged down and stalled again. It did not do this with the other fuel pump. I also changed the fuel filter. Normallyl it would just go through this without even a strain. Any suggestions????